The present invention relates to a diagnosis system for a motor vehicle and more particularly to a system where data formats are provided and a format for a vehicle to be diagnosed is properly selected.
Recently, a motor vehicle has been equipped with an electronic control system for controlling various components of an engine, such as fuel injectors, thereby improving driveability, exhaust gas emission, fuel consumption, and engine power. The electronic control system controls the components based on information represented by output signals from various sensors for detecting engine operating conditions. Accordingly, if malfunctions of components and sensors occur, the engine does not properly operate.
However, because of the complexity of the electronic control system, it is difficult to immediately find out the trouble. Accordingly, a trouble diagnosis device for easily checking the electronic control system should be equipped in an auto shop.
Japanese Patent Application Laid-Open No. 58-12848 discloses a diagnosis system in which an exclusive checking device is provided for measuring a pulse duration of fuel injection and engine speed, and for checking whether idling speed is normal.
Generally, data are transmitted between the diagnosis device and the control system provided in the vehicle in accordance with only one data format. For example, a data format F1 as shown in FIG. 4a is used for transmitting data such as coolant temperature and battery voltage one by one.
Since data of the coolant temperature and the battery voltage do not change much in a short period, the time for processing data is not delayed even if the data are transmitted by only one data format.
However, data such as the fuel injection pulse width of an engine varies with engine operating conditions such as engine speed and load of the engine. Therefore, it is necessary to measure data for the engine operating conditions as well as the fuel injection pulse width.
Heretofore, data for the fuel injection pulse width or the engine operating conditions are transmitted in accordance with one data format. Accordingly, it takes a long time to transmit data and hence to diagnose the vehicle.